When harvesting grains and the like, it is a known practice to chop up the straw portion for redistribution over the ground. Redistributing the chopped up straw on the ground assists in maintaining moisture in the ground and also acts to return some nutrients back to the ground. In light soils, disc units are generally known to be effective to incorporate the straw into the soil and further break-up the straw to aid in its incorporation back into the soil. In heavier soils, for example clay type soils, known straw chopper attachments for combines and the like are generally known to not chop the straw finely enough to be effectively incorporated back into the soil by subsequent agricultural operations. The straw then interferes with subsequent seeding operations when replanting a new crop, and must be removed or burned.
U.S. Pat. Nos. 6,070,816 to Hirsch and 6,616,528 to Wolters et al. disclose examples of straw chopper attachments for a combine in which a pair of rotors carrying blades thereon are mounted for rotation about respective vertical axes in opposing directions. The rotors are positioned adjacent the discharge of the combine so that the straw must pass through the rotors to be distributed onto the fields. The configuration of the rotors readily permits straw to pass through the housing of the rotors in a single pass so that the straw is not necessarily effectively chopped.
U.S. Pat. No. 6,550,231 to Krone et al. discloses a harvesting machine comprising a self-propelled pickup chopper intended for chopping straw, however the machine involves a very complex arrangement of parts in order to effect this task.